The present invention relates to an apparatus for magnetically transferring servo data for positioning the magnetic head for data recording and for data reading to a magnetic disc (magnetic recording medium) in a hard disc drive (hereinafter referred to as a xe2x80x9cHDDxe2x80x9d), that is typically utilized in a peripheral storage apparatus for most computers. Specifically, the present invention relates to a magnetic transfer apparatus, that uses the magnetic transfer techniques for transferring servo data to the so-called perpendicular magnetic recording media, in that the direction of the magnetization recorded therein is perpendicular to the magnetic recording media.
The magnetic recording media used for HDD""s exhibit a recording density of 20 Gbit per a square inch at the present stage of development and the recording capacity thereof is increasing at the rate of 60% a year. Since the area for recording one bit has become narrower due to the increase of the recording capacity, data recording and data reproduction by the so-called longitudinal magnetic recording method, in that the direction of the magnetization recorded is parallel to the surface (longitudinal direction) of the magnetic recording medium, has become more difficult. To obviate this problem, a so-called perpendicular recording medium, in that the direction of the magnetization recorded is perpendicular to the magnetic recording medium, has been proposed. The perpendicular magnetic recording medium includes a magnetic recording layer of a hard magnetic material and a lining layer of a soft magnetic material for localizing the magnetic fluxes generated by the magnetic head used for recording data in the recording layer.
In the usual HDD""s, data is recorded and reproduced by a magnetic head mounted on a floating mechanism called slider, that keeps the magnetic head floating several tens of nanometers above a circular magnetic recording medium rotating. The bit data on the magnetic recording medium is stored in data tracks arranged concentrically on the magnetic recording medium. To record and reproduce data, the magnetic head for data recording and for data reproduction is moved quickly toward an aimed data track and positioned above the aimed data track. Servo data including tracking signals for detecting a relative position of the magnetic head and the data track, address signals and reproducing clock signals are stored on the recording plane of the magnetic recording medium. The servo data corresponding to one data track is stored on the same circle of the data track at a predetermined period of angles. As shown in FIG. 17, the servo data is stored in servo data regions, shaped with stripes (or fans) and formed at a predetermined period of angles, and along the data tracks. The servo data is recorded by an exclusive apparatus called servo track writer to a magnetic recording medium mounted on a HDD, so that the centers of the regions storing the signals indicative of the servo data may not deviate from the center of the magnetic recording medium nor from the center of the trajectory of the magnetic head for data recording and for data reproduction.
As described earlier, the recording density of the servo data is inevitably rising with increasing recording density of the magnetic recording medium. Due to the high recording density of the magnetic recording medium, the time necessary to write the servo data with a high density is prolonged, the manufacturing efficiencies of the HDD""s are lowered and the manufacturing costs are increased.
Recently, an alternative method has been proposed to obviate the problems of the conventional method, which writes the servo data from a magnetic head of the data track writer for writing the signals indicative of the servo data in the data tracks track by track. The alternative method shortens the time necessary to record the servo data on magnetic recording media by transferring the servo data stored on a master disc to the magnetic recording media recording medium by recording medium by the magnetic transfer techniques.
Japanese Unexamined Laid Open Patent Application H10-40544 discloses a method of transferring servo data to a longitudinal magnetic recording medium from a master disc including convex portions and ferromagnetic concave portions. This publication, however, describes nothing on the magnetic transfer method for perpendicular magnetic recording media. Japanese Unexamined Laid Open Patent Application H11-25455 discloses a scheme that uses a master disc including a groove formed thereon for air feeding and for air sucking to ensure tight contact of the master disc with a magnetic recording medium. This publication, however, describes nothing on the magnetic transfer method for perpendicular magnetic recording media.
FIG. 1(a) is a schematic drawing describing initialization of a longitudinal magnetic recording medium. FIG. 1(b) is a schematic drawing describing magnetic transfer to the longitudinal magnetic recording medium. Referring now to FIG. 1(a), the initialization of the longitudinal magnetic recording medium is an operation that magnetizes the magnetic layer of a magnetic recording medium 1 in a certain direction parallel to the magnetic recording medium by a leakage magnetic field 4 leaking from a gap 3 of a ring head 2. Referring now to FIG. 1(b), the magnetic transfer is an operation, that applies a magnetic field 7, opposite to the leakage magnetic field 4 used in the initialization operation, from a gap 6 of a ring head 5 to the magnetic recording medium 1 in tight contact with a master disc for magnetic transfer 8 (hereinafter referred to simply as a xe2x80x9cmaster discxe2x80x9d). Since the leakage magnetic field 7 converges to soft magnetic layers 9 with a high magnetic permeability, the strength of the leakage magnetic field 7 applied to the magnetic recording medium 1 decreases in the portions facing to the soft magnetic layers 9 of the master disc 8. The strength of the leakage magnetic field 7 applied to the magnetic recording medium 1 does not decrease in the portions not facing to the soft magnetic layers 9. Therefore, only the portions of the magnetic recording medium 1 not facing to any soft magnetic layer 9 are magnetized by the leakage magnetic field 7. Thus, servo signals are transferred. As described above, the initialization operation or the transfer operation is conducted by positioning a ring head above one surface of a magnetic recording medium.
FIG. 2(a) is a schematic drawing describing initialization of a perpendicular magnetic recording medium, the magnetization direction thereof is perpendicular thereto. FIG. 2(b) is a schematic drawing describing magnetic transfer onto the perpendicular magnetic recording medium. Referring now to FIG. 2(a), a perpendicular magnetic recording medium 11 is initialized by a perpendicular magnetic field 14 applied thereto from two permanent magnets of single pole type 12 and 12 (hereinafter referred to as xe2x80x9csingle-pole magnetic headsxe2x80x9d) such that the magnetization directs to a direction perpendicular to the perpendicular magnetic recording medium 11. Referring now to FIG. 2(b), a perpendicular magnetic field 15, the direction thereof is opposite to that of the perpendicular magnetic field 14 used for initialization, is applied to the perpendicular magnetic recording medium 11 in tight contact with a master disc 8. The perpendicular magnetic field 15 converges to soft magnetic layers 9, the magnetic permeability thereof is high. The strength of the perpendicular magnetic field 15 increases in the portions of the perpendicular magnetic recording medium 11 facing to the soft magnetic layers 9 embedded in the master disc 8. The strength of the perpendicular magnetic field 15 decreases in the portions of the perpendicular magnetic recording medium 11 not facing to any soft magnetic layer 9. Therefore, the perpendicular magnetic field 15 is effective only beneath the soft magnetic layers 9 for magnetically transferring of the servo signals. In the way different from the magnetic transfer to the longitudinal magnetic recording medium, the magnetic transfer to the perpendicular magnetic recording medium is conducted with two single-pole magnetic heads 12, 12 or 13, 13 facing opposite to each other across the perpendicular magnetic recording medium 11.
The conventional magnetic transfer apparatus, that conducts magnetic transfer to the perpendicular magnetic recording medium, poses several problems. First, the magnetic field distribution in the magnetic transfer described with reference to FIG. 2(b) is explained. In the initialization described in FIG. 2(a) and the magnetic transfer in FIG. 2(b), two single-pole magnetic heads are arranged such that a pole of a first polarity of one of the magnetic heads is facing to a pole of a second polarity of the other magnetic head (1) to narrow the expansion of the magnetic field in the longitudinal directions and (2) to apply only the perpendicular component of the magnetic field to the perpendicular magnetic recording medium. FIG. 4 is a schematic drawing describing a model of the magnetic field applied by two single-pole magnetic heads 13 and 13. To simplify the model, it is assumed that only parallel components 21 and 22 exist on both sides of one of the single-pole magnetic heads 13 and only a perpendicular component 23 in the central area below the one of the single-pole magnetic heads 13. It is also assumed that only parallel components 24 and 25 exist on both sides of the other one of the single-pole magnetic heads 13 and only a perpendicular component 26 in the central area above the other one of the single-pole magnetic heads 13. As the model described in FIG. 4 indicates, the single-pole magnetic heads 13 and 13 positioned facing to each other are more effective to converge the perpendicular components 23 and 26 and to prevent the parallel components 21, 22, 24 and 25 from extending as compared with using one single-pole magnetic head (e.g. one of the single-pole magnetic heads 13 only). When the single-pole magnetic heads 13 and 13 are aligned at the same orientation in perpendicular to the perpendicular magnetic recording medium 11 and spaced apart from the perpendicular recording medium 11 for the same distance (hereinafter, the above described arrangement of the magnetic heads will be referred to as the symmetrical positional relationship between (of) the magnetic headsxe2x80x9c), only the perpendicular components of the magnetic fields are applied to the perpendicular magnetic recording medium and the parallel components 21, 22 of the magnetic field applied by the one of the single-pole magnetic head 13 and the parallel components 24, 25 of the magnetic field applied by the other one of the single-pole magnetic head 13 compensate each other.
As described above, only the perpendicular components of the magnetic fields are effective for magnetic transfer to the perpendicular magnetic recording medium. Therefore, it is necessary not only for the physical shapes of the single-pole magnetic heads to be the same but also for the positional relationship between the magnetic heads to be symmetric with respect to the surface of the perpendicular magnetic recording medium.
Note that two single-pole magnetic heads are facing to each other in such an orientation that a pole of a first polarity of one of the magnetic heads is facing to a pole of a second polarity of the other magnetic head. Since the single-pole magnetic heads are spaced apart from the surface of the perpendicular magnetic recording medium for 0.5 mm at the shortest, the single-pole magnetic heads are spaced apart from each other for several mm. Since the single-pole magnetic heads exhibiting the magnetic force of the order of 10xe2x88x921 T (several thousands Gauss) or more are used in the conventional magnetic transfer apparatus, a stronger magnetic field may be used in the future. Therefore, a strong attractive force is generated between the single-pole magnetic heads. The strong attractive force causes a heavy load on the mounts of the magnetic heads. As described above, it is necessary to position the magnetic heads symmetrically with respect to the surface of the perpendicular magnetic recording medium. It is difficult and impractical to adjust the positions of the single-pole magnetic heads as described above depending solely on the mechanical precision of the single-pole magnetic heads. To obviate this problem, it is necessary to mount the single-pole magnetic heads on the magnetic transfer apparatus via an adjusting stage for adjusting the positions of the single-pole magnetic heads at least in one direction. However, the adjusting stage, that endures the heavy load described above, is inevitably large and such a large adjusting stage is impractical. Such a large adjusting stage is impractical also from the view point of costs. In view of the foregoing, it would be desirable to provide a magnetic transfer apparatus that meets the requirements of the rigidity of the mount of the single-pole magnetic head and includes a small adjusting stage for adjusting the positions of the single-pole magnetic heads.
For conducting a practical magnetic transfer operation, the perpendicular magnetic recording medium is attached to and detached from magnetic transfer apparatus. During the attaching and the detaching of the perpendicular magnetic recording medium, it is necessary to withdraw the magnetic heads from the perpendicular magnetic recording medium. It is necessary for the magnetic transfer apparatus to have a structure that facilitates moving the magnetic heads while keeping their symmetrical positional relationship during the removal thereof.
FIGS. 6(a) and 6(b) show the servo signals, that do not meet the transfer conditions described above. As described above, it is necessary to raise and lower the magnetic heads in the directions 10 shown in FIGS. 2(a) and 2(b) once for every turn of the magnetic recording medium to withdraw the magnetic heads from the perpendicular magnetic recording medium during the initialization and the magnetic transfer. In detail, FIG. 6(a) is a chart describing the waveform of the servo signal transferred by single-pole magnetic heads moved without their symmetrical positional relationship maintained during the magnetic transfer. FIG. 6(b) is a chart describing the wave form of a servo signal transferred, by single-pole magnetic heads moved with their symmetrical positional relationship maintained during the magnetic transfer, to the perpendicular magnetic recording medium initialized with the single-pole magnetic heads moved without their symmetrical positional relationship maintained during the initialization. When the magnetic heads for magnetic transfer are not moved symmetrically, an anomaly 34, that is a drastic change in the transferred signal intensity, is caused as shown in FIG. 6(a) once for every rotation cycle of the recording medium at the position of the recording medium, at that the magnetic heads for magnetic transfer are raised and lowered. Referring now to FIG. 6(b), an anomaly 35, that is a drastic change in the transferred signal intensity, is caused once for every rotation cycle of the recording medium at the position of the recording medium, at that the magnetic heads for magnetic transfer are raised and lowered. As the waveforms described in FIGS. 6(a) and 6(b) indicate, it is important to move the magnetic heads with their symmetrical positional relationship always maintained.
In view of the foregoing, it would further be desirable to provide a magnetic transfer apparatus for perpendicular magnetic recording media, and a method of magnetic transfer, that facilitates positioning magnetic heads symmetrically and moving the magnetic heads with their symmetrical positional relationship always maintained.
According to a first aspect of the invention, there is provided a magnetic transfer apparatus, the magnetic transfer apparatus magnetically transferring servo data carried by a master disc to a perpendicular magnetic recording medium including a substrate and a magnetic recording layer on the substrate, the magnetic transfer apparatus including: a positioning means, the positioning means positioning the master disc in close proximity to or in tight contact with the perpendicular magnetic recording medium; an adjusting means, the adjusting means adjusting the positions of the master disc and the perpendicular magnetic recording medium; a first magnetic field application means, the first magnetic field application means applying a magnetic field for magnetically transferring to the master disc and the perpendicular magnetic recording medium positioned in close proximity to each other or in tight contact with each other; the first magnetic field application means including a pair of magnetic transfer heads arranged symmetrically with respect to the surface of the perpendicular magnetic recording medium facing to the master disc; and the magnetic transfer heads moving symmetrically with respect to the surface of the perpendicular magnetic recording medium facing to the master disc.
Advantageously, the magnetic transfer apparatus further includes a second magnetic field application means, the second magnetic field application means applying to the perpendicular magnetic recording medium a magnetic field for initializing the magnetization over the entire perpendicular magnetic recording medium; the second magnetic field application means including a pair of magnetic initializing heads arranged symmetrically with respect to the surface of the perpendicular magnetic recording medium, that will be facing to the master disc; and the magnetic initializing heads moving symmetrically with respect to the surface of the perpendicular magnetic recording medium, that will be facing to the master disc.
According to a second aspect of the invention there is provided a magnetic transfer apparatus, the magnetic transfer apparatus magnetically transferring servo data carried by a master disc to a perpendicular magnetic recording medium including a substrate and two magnetic recording layers on the major surfaces of the substrate, the magnetic transfer apparatus including: a positioning means, the positioning means positioning the master disc in close proximity to or in tight contact with the perpendicular magnetic recording medium; an adjusting means, the adjusting means adjusting the positions of the master disc and the perpendicular magnetic recording medium; a first magnetic field application means, the first magnetic field application means applying a magnetic field for magnetically transferring to the master disc and the perpendicular magnetic recording medium positioned in close proximity to each other or in tight contact with each other; the first magnetic field application means including a pair of magnetic transfer heads arranged symmetrically with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; and the magnetic transfer heads moving symmetrically with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium.
Advantageously, the magnetic transfer apparatus further includes a second magnetic field application means, the second magnetic field application means applying to the perpendicular magnetic recording medium a magnetic field for initializing the magnetization over the entire perpendicular magnetic recording medium; the second magnetic field application means including a pair of magnetic initializing heads arranged symmetrically with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; and the magnetic initializing heads moving symmetrically with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium.
Advantageously, the first magnetic field application means includes a horizontal linear stage moving horizontally; two vertical linear stages moving vertically; two links connecting the horizontal linear stage and the vertical linear stages; the magnetic transfer heads being mounted on the respective vertical linear stages; and an actuator, the actuator driving the horizontal linear stage to move the magnetic transfer heads always symmetrically.
Advantageously, the first magnetic field application means includes a driving shaft; a pinion on the drive shaft; two racks coupled to the pinion, the racks being moved by the rotation of the pinion to the respective directions opposite to each other; two vertical linear stages fixed to the respective racks, the vertical linear stages moving vertically; the magnetic transfer heads being mounted on the respective vertical linear stages; and the driving shaft rotating to move the magnetic heads vertically and always symmetrically.
Advantageously, the first magnetic field application means includes a first linear stage; a second linear stage; the first linear stage and the second linear stage moving always symmetrically the magnetic transfer heads; the first linear stage including an adjusting stage mounting one of the magnetic transfer heads thereon, and a fixing means; the other one of the magnetic transfer heads being mounted on the second linear stage; the one of the magnetic transfer heads being released from the fixing thereof to the first linear stage to adjust the positions of the magnetic transfer heads; and the fixing means fixing the one of the magnetic transfer heads to the first linear stage to apply a magnetic field to the perpendicular magnetic recording medium.
Advantageously, the first magnetic field application means and the second magnetic field application means has the same structure.
Advantageously, each of the magnetic transfer heads is a single-pole magnetic head.
Advantageously, each of the magnetic transfer heads is a ring head.
Advantageously, each of the magnetic initializing heads is a single-pole magnetic head.
Advantageously, the master disc includes a nonmagnetic substrate including soft magnetic layers, the soft magnetic layers being arranged in stripe-shaped ranges patterned or embedded in the surface portion of the nonmagnetic substrate corresponding to the servo data.
According to a third aspect of the invention, there is provided a method of magnetically transferring servo data carried by a master disc to a perpendicular magnetic recording medium including a substrate and a magnetic recording layer on one of the major surfaces of the substrate, the method including the steps of: positioning the master disc in close proximity to or in tight contact with the perpendicular magnetic recording medium; positioning a pair of magnetic transfer heads in a symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium facing to the master disc; making the magnetic transfer heads come close to the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium facing to the master disc; applying a magnetic field to the perpendicular magnetic recording medium from the magnetic transfer heads to transfer the servo data from the master disc to the perpendicular magnetic recording medium; and withdrawing the magnetic transfer heads from the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium facing to the master disc.
Advantageously, the method further includes the steps of: positioning a pair of magnetic initializing heads the perpendicular magnetic recording medium in a symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium, that will be facing to the master disc; making the magnetic initializing heads come close to the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium, that will facing to the master disc; applying a magnetic field to the perpendicular magnetic recording medium from the magnetic initializing heads to initialize the perpendicular magnetic recording medium; and withdrawing the magnetic initializing heads from the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the surface of the perpendicular magnetic recording medium, that will be facing to the master disc.
According to a fourth aspect of the invention, there is provides a method of magnetically transferring servo data carried by a master disc to a perpendicular magnetic recording medium including a substrate and two magnetic recording layer on both major surfaces of the substrate, the method including the steps of: positioning the master disc in close proximity to or in tight contact with the perpendicular magnetic recording medium; positioning a pair of magnetic transfer heads in a symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; making the magnetic transfer heads come close to the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; applying a magnetic field to the perpendicular magnetic recording medium from the magnetic transfer heads to transfer the servo data from the master disc to the perpendicular magnetic recording medium; and withdrawing the magnetic transfer heads from the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium.
Advantageously, the method further includes the steps of: positioning a pair of magnetic initializing heads the perpendicular magnetic recording medium in a symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; making the magnetic initializing heads come close to the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium; applying a magnetic field to the perpendicular magnetic recording medium from the magnetic initializing heads to initialize the perpendicular magnetic recording medium; and withdrawing the magnetic initializing heads from the perpendicular magnetic recording medium while keeping the symmetrical positional relationship with respect to the center plane between the major surfaces of the perpendicular magnetic recording medium.
Advantageously, the pair of the magnetic transfer heads is a pair of single-pole magnetic heads, a pole of a first polarity of one of the single-pole magnetic heads facing to a pole of a second polarity of the other one of the single-pole magnetic heads.
Advantageously, the pair of the magnetic transfer heads is a pair of ring heads, the poles of the same polarity of the ring heads facing to each other.